Dry-running piston compressor (crankshaft drive lubrication)

ABSTRACT

The invention relates to a dry-running piston compressor, in particular for rail vehicles. Said compressor comprises a crankcase ( 3 ) for a crankshaft ( 15 ) that is rotatably mounted in said crankcase, the latter being provided with at least one pot-type cylinder ( 4   a   –4   c ) comprising a corresponding internal piston ( 12   a   , 12   e ). According to the invention, the crankshaft ( 15 ) is connected to one end of a connecting rod ( 14   a   , 14   c ) by means of a connecting rod hearing ( 16 ), which forms the first hearing point, in order to convert the rotational displacement into a linear displacement for the piston ( 12   a   , 12   c ) that is mounted at the other end of the connecting rod ( 14   a   , 14   c ) by means of a piston pin bearing ( 17 ), which forms the second bearing point. At least one lubricating nipple ( 18   a   , 18   c ) is mounted on the exterior of each connecting rod ( 14   a   , 14   c ) for relubricating the bearing point(s). A corresponding internal lubrication channel ( 22 ) runs from said nipple and discharges onto the connecting rod ( 16 ) and/or onto the piston pin bearing ( 17 ).

The invention relates to a dry-running piston compressor, particularlyfor rail vehicles, having a crankcase for a crankshaft rotatably mountedtherein, on which crankcase at least one pot-type cylinder having anassigned internal piston is arranged, the crankshaft being connected byway of a connecting rod bearing as a first bearing point with one end ofa connecting rod in order to convert the rotating movement in a linearmovement for the piston mounted at the other end of the connecting rodby means of a piston pin bearing as the second bearing point.

Conventionally, a separate drive unit is fastened to such a pistoncompressor of the above-mentioned type for generating a rotatingmovement for the crankshaft. Usually, an electric motor or the like isused as the drive unit. The piston compressor, which so far is composedof the piston compressor and the drive unit is used, for example, in thevehicle field for generating compressed air which is required for theoperation of vehicle-specific pressure medium aggregates—such as brakesor the like.

The piston compressors used in the vehicle field are conventionallysubjected to a long continuous operation or to a frequent switching-onand switching-off, which, as a result of friction, leads to a high heatdevelopment. In this field of application, oil-lubricated pistoncompressors have therefore predominantly been used which, if required,have a sufficient dissipation of excessive heat by way of an oil coolingcircuit for ensuring an always optimal operating temperature.

Recently, dry-running piston compressors have also been used in variousindustries. A dry-running piston compressor operates without lubricatingoil situated in a housing. Instead, the lubrication at the pistonrunning path is replaced by a particularly low-friction dynamic sealingarrangement. Furthermore, all rotating components are disposed in rollerbearings. In this case, the encased roller bearings are provided with atemperature-stable long-lifetime grease filling. In the valve region,slidingly guided components are largely avoided. As a result of the sumof these measures, an oil lubrication in the piston compressor is notnecessary. Consequently, for example, the risk of a fouling of thecompressed air generated by the piston compressor can be excluded.Furthermore, as a result of the elimination of an oil circuit and ofmajor additional compensating masses, a dry-running piston compressorcan be constructed to be of a relatively light weight.

The present invention relating to a dry-running piston compressor can beused in very different cylinder arrangements at the crankcase, such as aV-arrangement or an arrangement in the manner of a in-line engine.Furthermore, the piston compressor can also be constructed in severalstages with a low-pressure stage and at least one additional nexthigh-pressure stage. In addition, a very different fastening to thevehicle is also possible, as, for example, hanging on the vehicle floor(underfloor), horizontally or vertically standing within the body of thevehicle (interior installation) or the like.

In the vehicle field, particularly in the case of rail vehicles, longrunning times and maintenance intervals of the piston compressor arerequired. Thus, a piston compressor used in the rail vehicleconstruction should not have to be overhauled until it has operated forat least 6 years, which corresponds to an average of approximately12,000 operating hours. This aspect has so far stood in the way of theuse of dry-running, that is, oil-free compressors in the vehicle field,because the grease use duration in the case of lifetime-lubricatedroller bearings is not sufficient in the temperature range customary incompressors in order to survive these maintenance intervals withoutdamage to the bearings. Even when the operating temperatures are loweredas a result of a multi-stage compression with an intermediate cooling,the lifetime of the grease will be limited. Furthermore, because of apoor accessibility within the crankcase, the regreasing of the bearingpoints presents problems. Another problem results from the fact thatgrease emerging during the regreasing may reach the cylinder runningsurfaces of the piston engine, which leads to increased wear at thedry-running piston rings and the piston coatings.

It is an object of the present invention to provide a long-lifedry-running piston compressor in the case of which an optimallubrication of the bearing points of the crankshaft drive is achieved ina simple manner.

Based on a dry-running piston compressor according to the preamble ofclaim 1, this object is achieved in connection with its characterizingfeatures. Additional measures improving the invention are indicated inthe dependent claims which follow.

The invention includes the technical teaching that, for the regreasingof the bearing points of the crankshaft drive, at least one lubricatingnipple is mounted on the outside on each connecting rod, from whichlubricating nipple, a corresponding internal lubricating duct extendswhich leads into the connecting rod bearing and/or into the crankshaftbearing.

The advantage of this solution, which can easily be implementedconstructively, is the fact that now a meterable regreasing of thebearing points is possible which are permanently lubricated per se. Itwas found that a lubricating duct extending inside the connecting roddoes not considerably impair the stability of the connecting rod in theoperation. The lubricating nipple is to be placed at the connecting rodsuch that a good accessibility exists from the outside.

The crankcase is preferably provided with at least one closable openingby way of which, by means of a lubricating tool, a feeding oflubricating medium takes place to the lubricating nipples from theoutside. In this case, the opening in the crankcase can be closed bymeans of a lid which is detachably fastened on the crankcase by means ofa screwed connection.

In the case of this above-described arrangement, the regreasing canparticularly advantageously take place manually by means of a meteringpress. A metering of the delivery quantity of lubricant can take placeby way of a shut-off valve. A refilling of lubricant can be implementedby way of an exchangeable grease cartridge. The grease metering presscan be driven electrically or can be operated manually by means of alifting device.

Advantageously, a tube-shaped attachment is constructed on thelubricating tool for delivering the lubricant. Since the lubricatingnipples are situated inside the crankcase, it may be advantageous tomount electrical illuminating devices on the lubricating tool forilluminating the regreasing area situated inside the ball housing.

It is particularly advantageous for the lubricating nipples to bearranged in the shaft area of the connecting rod because, in the case ofthis placement, a particularly good accessibility can be implemented byway of the opening in the crankcase. This particularly applies to anessentially horizontal arrangement of the crankshaft drives in thecrankcase.

The lubricating duct starting out from the lubricating nipple canadvantageously be produced in the form of a single passage bore whichextends through the shaft and which is separated by means of a closingbody into two partial ducts each assigned to a bearing point. In thiscase, a separate lubricating nipple is also assigned to each partialduct. The closing body is preferably constructed as a ball element whichis pressed into the passage bore constructed in the manner of an offsetbore in the area of the step. As an alternative, it is also conceivableto produce the lubricating duct in the form of two basic bores extendingalong the shaft, which basic bores each lead to a bearing point and toeach of which a separate lubricating nipple is assigned. It is alsoadvantageous for a grease collecting space to be provided in theconnecting rod in the area of the connecting rod bearing and/or in thearea of the crankshaft bearing, for storing lubricant. As a result, onthe one hand, a supply of sufficient lubricant can be created for thebearing point to be supplied and, at the same time, an undesirableemerging of lubricant from the bearing area can be prevented.

Additional measures improving the invention are illustrated in detail inthe following by the description of a preferred embodiment of theinvention by means of the figures.

FIG. 1 is a perspective outside view of a dry-running piston compressorwith the drive unit, which form a piston compressor used in the railvehicle construction;

FIG. 2 is a longitudinal sectional view of a connecting rod of acrankcase of the piston compressor according to FIG. 1; and

FIG. 3 is a cross-sectional view of the piston compressor according toFIG. 1 in the area of two opposite cylinders.

A dry-running piston compressor according to FIG. 1 essentially consistsof a 2-stage compressor unit 1 with a flanged-on drive unit 2. The driveunit 2 is constructed as an electric motor and is detachably fastened tothe crankcase 3 of the compressor unit 1 by means of a screwedconnection. The drive unit 2 causes a crankshaft arranged in thecrankcase 3 but not visible here to carry out a rotating movement whichis converted to a stroke movement for pistons which are housed insidethe pot-type cylinders 4 a–4 c fastened on the crankcase 3, forgenerating compressed air. By means of the piston stroke movement, airis taken in from the atmosphere by way of an input-side filterarrangement 5 and is compressed in stages inside the cylinders 4 a–4 c.The thus generated compressed air passes through a cooler arrangement 6and is then available to the compressed-air system of a rail vehicle byway of the connection 7.

In this embodiment, the compressor unit 1 is constructed as amulti-stage piston compressor with a low-pressure stage and ahigh-pressure stage. The cylinders 4 b and 4 c are assigned to thelow-pressure stage; the cylinder 4 a is part of the high-pressure stage.All cylinders 4 a–4 c are arranged on the crankcase 3 of the compressorunit 1 in an opposed manner in a 180° V-construction. For fastening thecompressor unit 1 with a flanged-on drive unit 2 to a carrierconstruction—not shown here in detail—of a rail vehicle, connectingdevices 8 are provided.

FIG. 2 is a view into the interior of the compressor unit 1, as anexample, in the area of the opposed cylinders 4 a and 4 c. The cylinders4 a and 4 c are each closed off on the face side by way of a valve plate9 a and 9 c by means of one cylinder head 10 a and 10 c respectively.One cylinder liner 11 a and 11 c respectively made of a minimal-frictionhard material is embedded in the cylinders 4 a and 4 c. In this cylinderliner 11 a and 11 c respectively, one piston 12 a and 12 c respectivelyis arranged which an be moved back and forth for generating compressedair. As the dynamic sealing device between the cylinder liner 11 a, 11 cand the assigned piston 12 a and 12 c respectively, a packing ring 13 aand 13 c respectively is provided within a groove-shaped recess on theupper edge area of the piston 12 a and 12 c respectively. The packingring 13 and 13 c also consists of a minimal-friction material. Thelinear drive of the pistons 12 a and 12 c takes place by way of a crankdrive by means of connecting rods 14 a and 14 c respectively. On theside situated opposite the pistons 12 a and 12 c, the connecting rods 14a and 14 c are connected with the crankshaft 15 by way of a connectingrod bearing 16. The piston-side fastening of the connecting rod 14 a, 14c takes place by way of an assigned piston pin bearing 17. Theconnecting rod bearing 16 as well as the piston pin bearing 17 areconstructed in the manner of a permanently lubricated roller bodybearing.

For the regreasing of the two bearing points, two lubricating nipples 18a, 18 c are in each case mounted on the outside of each connecting rod14 a, 14 c. On the lower side, the crankcase 3 is provided with twoopenings 19 a, 19 c each assigned to a connecting rod 14 a and 14 b, bywhich openings 19 a, 19 c, by a lubricating tool 20, lubricant can besupplied to the lubricating nipples 18 a and 18 c from the outside. Theopenings 19 a and 19 c in the crankcase 3 can each be closed off by alid 21, shown in opening 19 c, which can be screwed in. An electricalilluminating device 30 may be provided on the lubricating tool 20. Thelubricating tool may be a grease metering press.

A lubricating duct 22 extends inside the connecting rod 14 illustratedin FIG. 3 as a component part. The lubricating duct 22 is constructed inthe form of a single passage bore extending through the shaft 23 of theconnecting rod 14. The passage bore is divided by a closing body 24 inthe form of a ball element into two partial ducts 22 a, 22 b eachassigned to a bearing point, a separate lubricating nipple—not shownhere—being assigned to each partial duct. In this case, one partial ductleads to the piston pin bearing 17; the other partial duct is assignedto the connecting rod bearing 16. In order to ensure a supply oflubricant to the connecting rod bearing 16 as well as to the piston pinbearing 17, diverse breakthroughs 25 are provided, in the external ringsof the connecting rod bearing 16 as well as of the piston pin bearing17, which connect the partial ducts to the area of the roller bodies.

List of Reference Numbers

-   Connection 8-   connection device 9-   lubricating tool 21

1. A dry-running piston compressor comprising: a crankshaft rotatably mounted in a crankcase; a connecting rod connecting the crankshaft by a rod bearing to at least one piston by a piston pin bearing; at least one lubricating nipple on the outside of the connecting rod; at least one lubricating duct interior to the connecting rod connecting the lubricating nipple to one of the bearings; the lubricating duct being a single passage bore which extends through a shaft of the connecting rod to both bearings and which is divided by a closing body into two partial ducts each assigned to a bearing; and a separate lubricating nipple is provided for each partial duct.
 2. The dry-running piston compressor according to claim 1, wherein the crankcase includes at least one opening for providing access of a lubricating tool, from the outside, to the lubricating nipple.
 3. The dry-running piston compressor according to claim 2, wherein the opening in the crankcase is closed off by a detachable lid.
 4. The dry-running piston compressor according to claim 2 wherein the lubricating nipple is arranged in a shaft area of the connecting rod.
 5. The dry-running piston compressor according to claim 1, wherein the passage bore is as an offset bore, in the area of a step; and a ball element is pressed in as the closing body.
 6. The dry-running piston compressor according to claim 1, wherein the lubricating duct is constructed as two separate bores which extend along a shaft of the connecting rod to both bearings and a separate lubricating nipple is provided for each of the bores.
 7. The dry-running piston compressor according to claim 1, including a grease collecting space, for storing lubricant, in the area of at least one of the bearings.
 8. The dry-running piston compressor according to claim 1, combination with a manual lubricating tool constructed as a grease metering press.
 9. The dry-running piston compressor according to claim 8, including an electrical illuminating device for illuminating a regreasing area situated inside the crankcase is mounted on the lubricating tool. 